The present invention generally relates to a local multipoint distribution service (LMDS) system or local multipoint communication system (LMCS), and more particularly to the base station architecture of the LMDS system.
The LMDS system provides a xe2x80x9cwireless local loopxe2x80x9d or the xe2x80x9clast milexe2x80x9d link to subscribers for fixed communication services such as video and telephony including data information such as facsimile and computer signals. The LMDS system includes a base station or node for sending and receiving selected communication signals to and from a customer premises equipment (CPE) which is remotely located with the subscribers. In addition to the CPE, the base station is also connected to a video serving office or other distribution centers for video content and to a central office switched telephony network for telephony services. A typical LMDS system consists of several base stations per central office and video serving office, and several thousand CPE sites per base station. In this manner, the LMDS system is a xe2x80x9cpoint-to-multipointxe2x80x9d cellular communication system, the base station being the point, and the CPE sites, the multipoint. The connection between the base station and the subscribers is generally through broadband radio frequency (RF). The bandwidth depends on the spectrum allocation but is generally about 1 GHz. The subscriber equipment or CPE tunes to one or more RF frequency channels within the 1 GHz band to connect to the base station.
It is cost effective to have the capacity of the base station correspond to the demand of the subscribers linked to the base station at a given time. However, it is difficult to predict the number of subscribers who will be linked to the base station, especially when the LMDS system is initially being implemented. Consequently, if the number of subscribers grows unexpectedly from the initially projected number, a conventional base station would not be capable of servicing all the subscribers without an extensive and time consuming reconfiguration of the base station, which is an expensive operation. On the other hand, if the number of subscribers predicted is too high or if a significant number of the subscriptions is canceled, the base station would operate at undercapacity.
Also, the conventional base stations generally include a base unit and a remote unit which are physically partitioned from each other. The remote unit includes an antenna which is located, for example, on a tower or on top of a building, and is connected to the other parts of the remote unit via a long wave-guide. A disadvantage of using a long wave-guide is that it is expensive and prone to excessive loss (approximately 15 dB/100 ft). Routing the wave-guide to the top of a building, for example, is also a difficult task.
Accordingly, it is a primary object of the present invention to provide an improved base station for cost effectively implementing an LMDS system.
Another object is to provide an improved base station having a base unit which has a modular configuration to allow operation of both small and large systems.
Still another object is to provide an improved base station having a modular configuration for grouping similar functions into proximately located shelves to minimize cabling and RF signal impairments.
A further object is to provide an improved base station having a remote unit which minimizes the length of the wave-guide between an antenna and the other remote unit electronics.
Yet another object is to provide an improved base station having a remote unit which integrates an antenna and the associated transmitter and receiver into a single assembly.